Greenhouse trace gases in deadwood

Deadwood, long recognized as playing an important role in storing carbon and releasing it as CO 2 in forest ecosystems, is more recently drawing attention for its potential role in the cycling of other greenhouse trace gases. Across three Northeastern and Central US forests, mean methane (CH 4 ) concentrations in deadwood were 23 times atmospheric levels (43.0 μL L −1 ± 12.3; mean ± SE), indicating a lower bound, mean radial wood surface area flux of ~6 × 10 −4 μmol CH 4 m −2 s −1 . Site, decay class, log diameter, and species were all highly significant predictors of CH 4 abundance in deadwood, and diameter and decay class interacted as important controls limiting CH 4 concentrations in the smallest and most decayed logs. Nitrous oxide (N 2 O) concentrations were negatively correlated with CH 4 (r 2 = −0.20, p < 0.001) and on average ~25 % lower than ambient (276.9 nL L −1 ± 2.9; mean ± SE), indicating net consumption of nitrous oxide. Oxygen (O 2 ) concentrations were uniformly near anaerobic (355.8 μL L −1 ±1.2; mean ± SE), and CO 2 was elevated from atmospheric (9336.9 μL L −1 ± 600.6; mean ± SE). Most notably, our observations that CH 4 concentrations were highest in the least decayed wood, may suggest that methanogenesis is not fuelled by structural wood decomposition but rather by consumption of more labile nonstructural carbohydrates.